【作者】 刘鹏飞；

【导师】 郭乙木；

【作者基本信息】 浙江大学 ， 工程力学， 2006， 博士

【摘要】 界面的破坏与失效是考察纤维增强复合材料产生增韧效应的关键力学问题。本文主要研究了SiC／Ti-Al复合材料和陶瓷基复合材料的基体裂纹沿界面的偏移、纤维桥联增韧机理。考察了界面断裂特性的纤维拔出、多纤维／基体复合材料的拉伸应力-应变特性和拉伸强度、单纤维断裂后引起的相邻纤维中的应力集中、随机纤维桥联疲劳寿命和可靠性等问题。具体研究成果如下： (1) 建立基体裂纹偏移／穿透有限元模型，并分析了相对裂纹扩展长度、材料参数、纤维体积分数对相对能量释放率的影响；给出了广泛使用的SiC／Ti-Al复合材料和陶瓷基复合材料最有利于基体裂纹偏移的弹性参数；并指出了含有纤维碳涂层时的优缺点。基于有限元结果和能量偏移准则，有效地评估了界面断裂韧性。 (2) 提出的桥联本构函数反映了桥联应力和基体裂纹展开位移之间无穷阶的非线性关系，且解释了桥联本构关系的上升和下降部分及其比率关系。通过计算桥联阻抗曲线，验证了纤维桥联中出现稳定基体裂纹增长阶段的物理特性；通过计算桥联载荷随基体裂纹长度的分布，证明桥联效应是纤维增强复合材料中主导的增韧机理；通过计算外载荷和载荷点位移的关系曲线，解释了从纤维桥联、纤维失效到纤维拔出的转换过程。 (3) 界面分离能释放率随界面分离长度的增加而减小。随分离界面摩擦应力的增加，纤维和基体剪切效应以及泊松效应抑制界面失效的能力增强，这是按剪滞理论所无法获得的结果。由纤维／基体热失配引起的热残余应力有利于抑制界面的失效。桥联本构关系(文[137，138]中)的幂指数n=0.5只适合于低摩擦应力和低界面断裂韧性的弱界面。 (4) 本文建立的有限元模型较好地模拟了复合材料拉伸破坏失效的过程，包括实时的界面分离和纤维断裂。GLS和HVDP模型在一定程度上低估了断裂纤维附近完整纤维中的应力集中。同时，由于热处理引起的热残余温度能改善复合材料的拉伸特性，进而提高复合材料最终拉伸强度。 (5) 在随机循环应力作用下，提出纤维桥联基体裂纹扩展的首次穿越扩散过程模型。证实了裂纹扩展尺寸对纤维桥联疲劳寿命和可靠性的影响。随基体裂纹扩展疲劳寿命和可靠性的分布呈现出两种不同的非线性下降特性。证明了韦布尔分布和对数正态分布对于模拟纤维桥联疲劳寿命随时间的分布具有一致性。更多还原

【Abstract】 The damage and failure of the interface is a crucial mechanical problem for exploring the toughening effect in fiber-reinforced composites. For the SiC/Ti-Al composite and ceramic matrix composite, the primary research of this paper concentrates mainly on the matrix crack deflection along the interface and the fiber-bridging toughening mechanism. The fiber pull-out for exploring the interfacial fracture properties, the tensile stress-strain properties of the multi-fiber/matrix composites and the tensile strength, the stress concentration on the intact fibers near a broken fiber as well as the stochastic fiber bridging fatigue lifetime and reliability are investigated. The detailed research results are expressed as:(1) The finite element model of matrix crack deflection/penetration is established and the effects on the relative energy release rate of the relative crack growth length, material parameters and fiber volume fraction are analyzed. The reason why the elastic parameters in the widely used SiC/Ti-Al composite and ceramic matrix composite favor the matrix crack deflection is given. The advantage and disadvantage of the fiber carbon coating are commonly pointed out. The interfacial fracture toughness is effectively evaluated based on the finite element results and the energy-based deflection criterion.(2) The presented bridging constitutive function reflects an infinite-order non-linear relationship between the bridging stress and the matrix crack opening displacement, and interpretes the increasing and decreasing parts as well as their respective fractions. A stable matrix crack growth stage appearing in fiber bridging is confirmed by calculating the bridging resistance curve. The fact that the fiber bridging effect is a dominating toughening mechanism in fiber-reinforced composites is confirmed by calculating the distributions of bridging loads with the matrix crack length. The transformation process from fiber bridging, fiber failure to fiber pull-out is interpreted by calculating the load-displacement curve.(3) The interfacial debonding energy decreases with increasing interface debond length. With increasing friction stress at the debonded interface, the abilities for the shear effects in the更多还原